Streets and intersections in urban areas, parking lots, parks and the like spaces are provided with outdoor illuminating devices such as street lights and security lights. While incandescent lamps, mercury-vapor lamps, fluorescent lamps and the like kinds have hitherto been used as the light sources of the outdoor illuminating devices, there is a rise of numerous ideas in recent years of illuminating devices using LEDs (“Light Emitting Diodes”) as the new light sources that replace the incandescent and the other conventional lamps.
Patent reference 1 discloses, as an example, an illuminating device using white LEDs as the light source and provided with a lampshade having a concaved shape with asperities formed on the surface facing the light source for the purpose of widening an area illuminated by the light of the LEDs (refer to patent reference 1).
In addition, patent reference 2 discloses another illuminating device comprising a wide-angle LED illuminator, a middle-angle LED illuminator and a narrow-angle LED illuminator, and the individual illuminators are arranged in a manner to direct the light toward different areas across a walkway (refer to patent reference 2).
The illuminating devices using LEDs for their light sources are practical for conducting various business activities with consideration given to the environment since they can cut back power consumption and achieve reduction of loads on the environment for prevention of global warming by virtue of low thermal dissipation from the light sources. These illuminating devices also draw attention for their high durability and wide variety of luminous colors of the light sources.
Incidentally, efforts are being made in recent years to reconsider the environmental design for establishing safe and secure communities. With regard to the outdoor illuminating devices, in particular, there is a growing interest in the work aimed to controlling (or, preventing) crimes in certain areas of the community by replacing the outdoor illuminating devices (especially the security lights) with those of “blue color”.
It is anticipated that provision of the security lights emitting “blue color” can prevent crimes in these areas for some conceivable reasons such as: (1) the blue color inherently has a sedative effect acting upon the parasympathetic nerves of humans as well as an effect of calming psychologically because of the general preference to it; and (2) the blue color mentally moves the potential criminals to “avoid being seen” due to the “Purkinje effect” that the blue color improves visibility in the nighttime as compared to red and orange colors.
Demonstrative experiments have already been carried out in many areas, and the interesting results have also been reported.
With the outdoor illuminating device of the conventional structure, however, there exists a problem even when the illumination light is changed simply to “blue color” that the solid blue color illuminated from the main lighting unit tends to produce uneven contrast of color tone on the ordinary road surface paved with asphalt, etc. of dark color, which has a contradicting effect of impeding the smooth traffic of pedestrians and passing vehicles in the area generally directly below the outdoor illuminating device.
There is also a problem when blue LEDs are mounted to the outdoor illuminating device of the conventional structure that it does not provide as much an effect of preventing crimes as anticipated since the directivity intrinsic to the LEDs is likely to cause color shading in certain directions of the illumination, which disturbs visually of the blue light for the pedestrians and passing vehicles at distant locations.
There are other structures as proposed by patent references 3 and 4, for instance, in the light of improving the visibility of illumination light for the passing vehicles and pedestrians at the distant locations (refer to patent references 3 and 4).
Patent reference 1: Japanese Patent, No. 3,498,290
Patent reference 2: Japanese Patent Unexamined Publication, No. 2004-116177
Patent reference 3: Japanese Patent Unexamined Publication, No. 1999-111019
Patent reference 4: Japanese Patent Unexamined Publication, No. 2003-203506